Has anyone upgraded their preamp with V-caps?

Pauly, have you had a chance to try the relatively new Sonicap Platinum caps? They are a hybrid teflon cap and their cost is about half of the V-cap.

http://soniccraft.com/sonicap_platinum.htm

I just replaced .1uf REL/Audiocap TFT coupling caps in my Atma-Sphere MP-1 LS with V-Cap TFTF. With just a few hours break-in, it's surprising how much better the V-Caps are than the REL and how big a difference there can be between one teflon cap and another. Furthermore, this swap made a greater improvement than replacing oil/paper coupling caps in my amp that I know to be inferior to REL TFT-- confirming perhaps the critical importance of the preamp in the system.

I can't speak about the teflon v-cap in output stage application but would like to comment that replacing 2 x 3,3uF Mundorf silver/gold recently in my Omega DUOs tweeter XO made a huge improvement. Very costly upgrade but worth every penny imo.
Duomile

Sherod, I have not heard Sonicaps. A couple of folks have recommended I try them.

Just a note to those thinking of making the change (which we think is very worthwhile)

Its a good idea not to change the value. Increasing the value to get more bass may cause the low frequency cutoff to go too low- lower than the power supply low frequency pole for example. This can result in low frequency instability or maybe just flabby bass.

Your 2nd best bet so far is the Mundorf, but if you are using the cap in an output section, consider that in due time most paper and oil parts will develop a small amount of electrical leakage, which can have disastrous effects on the bias of power tubes!

The following applies to all Teflon caps:

Don't try to cut it close on the voltage ratings. Our experiences with several Teflon types is that is asking for the cap to short! Leave plenty of leeway for the voltage rating, and don't forget that during warmup the voltages across the cap will be equal to the voltage of the unloaded power supply!

Finally, do not give the part a lot of handling. Teflon does not 'cure' like polystyrene and polypropylene, so handling the part can cause the dielectric to pull away from the ends of the parts, changing its value or even shorting it. Once in circuit they are fine.